The purpose of this study is to compare the cecal intubation rate between two endoscopy water pump with different flow rates (1.7 ml/sec vs 10.4 ml/sec) in water immersion colonoscopy examination in unsedated patients undergoing diagnostic colonoscopy.

Inclusion Criteria:

• Adult > 18 years old with indication for colonoscopy, such as chronic diarrhea, chronic constipation, hematochezia, chronic lower abdominal pain, positive fecal occult blood test, and other change of bowel habit symptoms indicative of need for diagnostic colonoscopy examination

Exclusion Criteria:

• Patients refuse to participate, patient with obstructive lesion in the colon distal of the cecum, patients with experienced of colon resection, hemodynamically unstable, severe cardiac disorders (such as acute myocardial infarction, unstable angina, malignant arrhythmia, and moderate to severe congestive heart failure), patients with fecal obstruction (whatever the causes) so that impossible to pass the scope through the obstructed segment.